F2L recognition: sorting the 41 cases

The 41 F2L cases look scary on a list and almost obvious on the cube. The reason: they fall into a few families based on two simple questions, and every case in a family is solved the same way. Recognising an F2L case means answering those two questions without thinking about it.

The two questions

Hold the cube with the white cross on the bottom and the slot you want to fill at the front right. Find the corner (white plus the colours of the front and right centres) and the edge (those two colours, no white).

1. Where is the corner? On top, or already down in the slot. If it is on top, which way does its white face: to the right, towards you, or up?
2. Where is the edge? On top (and on which side of the corner), or already in the slot (the right way round, or flipped)?

The answers give you the family. The app names every case with exactly these two answers: “F2L 14 · Corner white up, edge at the back”, “F2L 31 · Corner down, white to the right, edge at the front”. The numbers are a reference point; the names are the recognition.

The families

Both pieces on top (F2L 1 to 24)

This is the vast majority of cases, and the family where intuition is almost always enough.

• White on the side, edge ready: the basic inserts, three moves (F2L 1 to 4). You see them at a glance: the corner and the edge are ready to go.
• White on the side, edge elsewhere: you need to move one of the two pieces a quarter turn of U before inserting, or split them and bring them back together (F2L 6, 7, 10, 11, 13, 15, 16, 18, 20, 21, 22, 24). Check whether the colours of the edge and the corner match where they touch: if the corner and edge sit side by side but the colours don’t line up, you have to split them.
• White facing up: the awkward family (F2L 5, 8, 9, 12, 14, 17, 19, 23). The corner isn’t ready for any insert; you have to tip it onto its side first. Spot this family by the white sticker showing on top: that’s your signal for “seven moves at least”.

F2L 1 · edge readyF2L 6 · edge elsewhereF2L 5 · white facing up

Edge in the slot, corner on top (F2L 25 to 30)

You see the edge in its slot (or flipped) and a white corner on top. Two sub-cases: the edge is the right way round (25, 26, 30) and a short algorithm brings the corner in; the edge is flipped (27, 28, 29) and you have to take it out at the same time. Check whether the front colour of the edge is on the front face.

F2L 25 · edge the right way roundF2L 27 · edge flipped

Corner down, edge on top (F2L 31 to 34)

The corner is in the slot but twisted (its white faces right or front instead of down). The edge is on top. Note which way the corner’s white faces: it tells you which move takes the corner out. These cases take six to eight moves, often better than pulling the corner out “by hand” and starting again.

F2L 31 · white to the rightF2L 33 · white to the front

Corner placed, edge elsewhere (F2L 35 to 37)

The corner is solved, white on the bottom and colours lined up. The edge is on top (35, 36) or in the slot but flipped (37). You have to take the corner out to fetch the edge, then put it back: that’s what the algorithms do, in eight moves.

F2L 35F2L 37

Both in the slot, wrongly placed (F2L 38 to 41)

Both pieces are there, but the corner is twisted and/or the edge is flipped. These are the longest and rarest cases: they almost never come up if you solved the earlier pairs cleanly, except on the last pair. Spot them by the fact that no piece of the pair is on top.

F2L 38F2L 40

Where to look

• White stickers first. There are only four white corners; the ones on top stand out straight away, and the direction their white faces (side or up) sorts the case.
• Then the corner’s sticker on top. If the white is on the side, the corner sticker on the top face tells you which edge to look for and which way round.
• The edge last. You know which colours you are after, so you scan the four top edges (and the bottom slots if needed).

With practice the order flips: you see an edge and a corner that belong together before you have even picked a slot, and you start with the easiest pair. That’s the goal: choose your pair rather than take whatever comes.

Spotting the cases you solve badly

After a few weeks of intuitive F2L, open the list of 41 cases in the app (the “F2L” step, or the Formulas sheet) and, for each case, compare the algorithm with what you usually do. Three outcomes:

• You do the same thing: great, move on.
• You take longer (an extra cube rotation, an insert followed by a fix): that’s a case to learn, and the algorithm replaces your detour.
• You don’t recognise the situation: it’s a rare case, note it down for later.

Usually there are about ten cases to learn, mostly in the “white facing up” family and among those where one piece is already in the slot. The other thirty you already solve fine.

F2L is easier to recognise from a distance than up close. If you have your nose against the cube hunting for pieces, hold it a little further away and take in the whole top layer: pairs are easier to see as a whole.